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Research Papers

A Novel Suction-Side Winglet Design Philosophy for High-Pressure Turbine Rotor Tips

[+] Author and Article Information
Chao Zhou

State Key Laboratory for Turbulence
and Complex Systems,
BIC-ESAT,
Collaborative Innovation Center
of Advanced Aero-Engine,
Peking University,
Beijing 100191, China
e-mail: czhou@pku.edu.cn

Fangpan Zhong

College of Engineering,
Peking University,
Beijing 100871, China
e-mail: zhongfp@pku.edu.cn

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received June 27, 2016; final manuscript received May 15, 2017; published online July 19, 2017. Editor: Kenneth Hall.

J. Turbomach 139(11), 111002 (Jul 19, 2017) (11 pages) Paper No: TURBO-16-1133; doi: 10.1115/1.4037056 History: Received June 27, 2016; Revised May 15, 2017

Winglet tips are promising candidates for future high-pressure turbine rotors. Many studies found that the design of the suction-side winglet is the key to the aerodynamic performance of a winglet tip, but there is no general agreement on the exact design philosophy. In this paper, a novel suction-side winglet design philosophy in a turbine cascade is introduced. The winglets are obtained based on the near-tip flow field of the datum tip geometry. The suction-side winglet aims to reduce the tip leakage flow particularly in the front part of the blade passage. It is found that on the casing endwall, the pressure increases in the area where the winglet is used. This reduces the tip leakage flow in the front part of the blade passage and the pitchwise pressure gradient on the endwall. As a result, the size of the tip leakage vortex reduces. A surprising observation is that the novel optimized winglet tip design eliminates the passage vortex and results in a further increasing of the efficiency. The tip leakage loss of the novel winglet tip is 18.1% lower than the datum cavity tip, with an increase of tip surface area by only 19.3%. The spanwise deflection of the winglet due to the centrifugal force is small. The tip heat load of the winglet tip is 17.5% higher than that of the cavity tip. Numerical simulation shows that in a turbine stage, this winglet tip increases the turbine stage efficiency by 0.9% mainly by eliminating the loss caused by the passage vortex at a tip gap size of 1.4% chord compared with a cavity tip.

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Figures

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Fig. 1

Comparison of turbulence model based on a low-speed flat tip, τ = 1.6%C: (a) velocity distribution of a low-speed flat tip, 35%Cy and (b) heat transfer coefficient

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Fig. 2

Cp0 distribution 35% axial chord downstream of cascade, flat tip, τ = 1.6%C: (a) exp. and (b) CFD

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Fig. 3

Validation of CFD tool based on transonic turbine cascades, τ = 1.6%C: (a) blade surface isentropic Mach number, exp. data from Zhang et al. [17] and (b) winglet tip heat transfer coefficient

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Fig. 4

Validation of CFD tool based on a winglet-cavity tip—Cp distribution on endwall, Zhou et al. [8]

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Fig. 5

Stagnation pressure coefficient at 45%Cx downstream trailing edge, τ = 1.9%C, Zhou et al. [8]: (a) flat, exp., (b) cavity, exp., (c) winglet, exp., (d) flat, CFD, (e) cavity, CFD, and (f) winglet, CFD

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Fig. 6

Tip geometries of cavity tip, winglet 1, and winglet 2: (a) cavity, (b) winglet 1 and (c) winglet 2

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Fig. 7

Mesh of winglet 1 with two cut planes near the tip

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Fig. 8

Mach number distribution on the middle tip gap plane: (a) design of winglet 1, with the baseline profile of cavity and (b) design of winglet 2, with the profile of winglet 1

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Fig. 9

Mach number distribution on the middle of tip gap of winglet 2

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Fig. 10

Normalized tip leakage mass flow rate that exit the tip gap

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Fig. 11

Static pressure coefficient distribution on casing endwall: (a) cavity and (b) winglet 2

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Fig. 12

Tip flow structure and dimensionless specific entropy increase of cavity tip and winglet 2: (a) cavity and (b) winglet 2

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Fig. 13

Tip flow structure and dimensionless streamwise vorticity distributions of cavity tip and winglet 2: (a) cavity and (b) winglet 2

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Fig. 14

Dimensionless specific entropy increase δs distribution on the plane of 0.5Cx downstream of the cascade: (a) cavity and (b) winglet 2

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Fig. 15

Pitchwise averaged δs along the span for cavity, winglet 1 and winglet 2

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Fig. 16

Constant-area mixing calculation

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Fig. 17

Tip leakage loss coefficients

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Fig. 18

Tip Nusselt number distribution: (a) cavity, (b) winglet 1 and (c) winglet 2

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Fig. 19

Normalized tip heat load

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Fig. 20

Distribution of spanwise deflection on the winglet 2 tip (mm)

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Fig. 21

von Mises stress distribution on the blade suction surface of (a) cavity, (b) winglet 1, (c) winglet 2, and (d) winglet 2 (smooth connection) (MPa)

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Fig. 22

Computational domain of the turbine stage

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Fig. 23

Comparison of winglet 2 tip geometries of cascade and stage

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Fig. 24

Dimensionless entropy increase distributions at different axial planes in the flow passage of rotor: (a) cavity and (b) winglet 2

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Fig. 25

Pitchwise-averaged dimensionless entropy increase along the span on plane 5 shown in Fig. 24

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